When turning ON/OFF a load that is driven by AC power, a ground fault strategy is performed entirely using a double-pole switch relay (switch). However, when there is a failure, such as the fusing of relay contact points it becomes impossible to control the supply of power to the load safely. For this reason, it is important to, for example, monitor for failures in the relay contact points, and the like, in order to guarantee the safety of the relay output.
Note that, as a method for detecting a relay failure, it has been proposed that a relay failure be detected through a logical process on a signal indicating the state of operation of a supplemental relay contact point and the input signal thereto, using a supplemental relay contact point (a second relay contact point) that is turned ON and OFF in addition to a primary relay contact point (a first relay contact point) that is turned ON and OFF by an input signal, as disclosed in, for example, Japanese Unexamined Patent Application Publication H3-273811 (“JP '811”).
However, in the method shown in JP '811, there is the problem of not being able to guarantee reliably the accuracy of the relay output because, for example, fault detection itself would become impossible if there were a failure in the fault detecting circuit that includes the supplemental relay contact point.
The present invention was created in such a situation, and the object thereof is to provide a relay failure detecting device wherein the stability of the relay output can be secured through reliably detecting faults in a relay circuit that supplies alternating current electric power through a double-pole switch relay to a load.